Gunmen kill Iraqi army colonel near Mosul

Earlier this month, a committee assigned to vet candidates for ties to Saddam's Baath Party said its list had grown to 511 names. The panel has not publicly released the roster of the blackballed candidates, which could include both Sunnis and Shiites accused of links to Saddam's regime.

But at least one person - a prominent Sunni lawmaker, Saleh al-Mutlaq - has complained he is banned from running.

"They are pulling people back to sectarianism," he said.

The tensions were further stoked Monday after a threat by officials in the southern city of Najaf to purge the province of Baathists.

The expulsions have not been carried out and the ultimatum was seen as a response to a series of deadly bomb attacks last week in the city, which holds important Shiite shrines and has close religious ties with neighboring Shiite power Iran. Saddam's regime included Shiites, but the Najaf order was widely portrayed by Arab media as a backlash specifically targeting the few Sunnis in the province.

A Sunni lawmaker, Osama al-Nujaifi, said the actions echo "the trials of the Middle Ages when they were trying people on suspicion without any concrete evidence."

Trying to find political common ground between Sunnis and Shiites is one of the vital elements in efforts to stabilize Iraq. On Sunday, Biden called Iraqi Prime Minister Nouri al-Maliki and other leaders to encourage a fair and inclusive election.

But the current pre-election discord has roots in U.S. decisions after Saddam's fall. Washington policy makers disbanded Saddam's Sunni-dominated security forces and bureaucracy as part of a top-to-bottom effort to sweep away supporters of his Baath Party - a move which opened the door for Shiites and Kurds to claim the greatest control.

Although Sunnis have rejoined the political process in recent years, there is lingering bitterness toward al-Maliki's government.

Sunni tribal leaders claim authorities have not followed through on promises for military and police posts for Sunni militia who joined the American-led fight against insurgents in one of the crucial turning points of the war. In Baghdad, many Sunnis were driven from their neighborhoods during the height of sectarian bloodshed in 2006-2008 when Iraq was pushed dangerously close to civil war.

The March election is seen as a chance for Sunnis to gain more seats in the expanded 323-seat parliament and have a greater role in running the country.

But there is still a climate of suspicion about a resurgence of possible Saddam loyalists.

Al-Maliki, a Shiite who is seeking re-election in March, has repeatedly accused Baathists of being responsible for major bombings last year that killed hundreds in Baghdad. The Iraqi government also has strained its relations with neighboring Syria over accusations it harbors former Saddam followers who have masterminded attacks in Iraq.

Some government critics have claimed that al-Maliki has pointed the finger at Baathists to divert attention from security failures, including blasts targeting government buildings. It also may be an attempt to undermine potential Sunni challengers.

The panel overseeing the political vetting is headed by Ahmed Chalabi, a Shiite who is blamed for supplying U.S. officials with faulty intelligence on Saddam's weapons program prior to the 2003 invasion.